Over the last few weeks I have monitored the accuracy of my GPS when augmented with satellite-based differential corrections. This system is called WAAS (Wide Area Augmentations System) in the US where it has been working for some time now, here in Europe it will be called EGNOS when finally finished, In the meantime the ESTB test bed has been working intermittently, and when doing so, the results have been very nice indeed:

Percentile Offset (meter)
67 1.1
95 2.1
99 2.8

I.e. over the last two weeks, 67 percent of all positions have been within about one meter, 95 percent within two and nearly all have been less than three meters away from the average (presumed correct) position.

This morning ESTB was again working, and for only the second time the geostationary satellite delivering the differential corrections was also giving ranging (i.e. position) data, so I had twelve working position channels, ten or eleven of them with differential corrections. This meant that a visit to the nearby ocean confluence would be able to get to the exact spot, with an accuracy better than two meters.

We left our summer harbour at Viker, near the southernmost point of the Asmaløy island, and sailed about 4-5 km until we got close to the point. We then lowered our sails, started the engine, and proceeded to steer across the point, both forwards, and while backing up. On our third attemp, where we steered a bit upwind of the point, then allowed the boat to mostly drift back, we finally hit the zero point.

The GPS indicated a final distance of 41 cm, which means that we got within 2 m with a probability of about 90%.

After getting the required photos we hoisted the sails again, and had an enjoyable afternoon in 12-16 knots of wind. There were many other boats in the area, since this is the main passage between Norway and Sweden here on the coast. Of all the boats tacking upwind, many must pass within less than 100 m, which means that they could all claim visits if they just knew about the project.